glibc/nptl_db/td_thr_tlsbase.c

/* Locate TLS data for a thread.
   Copyright (C) 2003-2014 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include "thread_dbP.h"

td_err_e
td_thr_tlsbase (const td_thrhandle_t *th,
		unsigned long int modid,
		psaddr_t *base)
{
  td_err_e err;
  psaddr_t dtv, dtvslot, dtvptr;

  if (modid < 1)
    return TD_NOTLS;

  psaddr_t pd = th->th_unique;
  if (pd == 0)
    {
      /* This is the fake handle for the main thread before libpthread
	 initialization.  We are using 0 for its th_unique because we can't
	 trust that its thread register has been initialized.  But we need
	 a real pointer to have any TLS access work.  In case of dlopen'd
	 libpthread, initialization might not be for quite some time.  So
	 try looking up the thread register now.  Worst case, it's nonzero
	 uninitialized garbage and we get bogus results for TLS access
	 attempted too early.  Tough.  */

      td_thrhandle_t main_th;
      err = __td_ta_lookup_th_unique (th->th_ta_p, ps_getpid (th->th_ta_p->ph),
				      &main_th);
      if (err == 0)
	pd = main_th.th_unique;
      if (pd == 0)
	return TD_TLSDEFER;
    }

  /* Get the DTV pointer from the thread descriptor.  */
  err = DB_GET_FIELD (dtv, th->th_ta_p, pd, pthread, dtvp, 0);
  if (err != TD_OK)
    return err;

  /* Find the corresponding entry in the DTV.  */
  err = DB_GET_FIELD_ADDRESS (dtvslot, th->th_ta_p, dtv, dtv, dtv, modid);
  if (err != TD_OK)
    return err;

  /* Extract the TLS block address from that DTV slot.  */
  err = DB_GET_FIELD (dtvptr, th->th_ta_p, dtvslot, dtv_t, pointer_val, 0);
  if (err != TD_OK)
    return err;

  /* It could be that the memory for this module is not allocated for
     the given thread.  */
  if ((uintptr_t) dtvptr & 1)
    return TD_TLSDEFER;

  *base = dtvptr;
  return TD_OK;
}